The present invention relates to a charger for charging a photosensitive drum of an image forming apparatus, and more particularly, to a brush contact charger for charging the surface of a photosensitive drum at a nearly uniform electrical potential in an image forming apparatus adopting a charging system that employs a brush contact method.
In an image-forming apparatus using electrophotography to form an electrostatic latent image, the image forming apparatus uses high voltage to uniformly charge a photosensitive drum, exposes the photosensitive drum, and then terminates the charge. Then, the latent image is developed by an electrically charged toner and the developed image is fixed to a print medium by heating and pressing.
Meanwhile, most image forming apparatuses in current use adopt a corona discharging system employing a high voltage application as the method for charging the surface of a photosensitive drum. The corona discharging system, however, generates ozone (O.sub.3), which causes environmental problems. Accordingly, a charging system employing a brush contact method has recently been under study.
Conventionally, a charger is electrically connected to a power supply and is installed so that a brush contacts a surface of a photosensitive drum which rotates together with a developing roller. Here, when voltage is applied from the power supply, the charger charges the surface of the photosensitive drum at a predetermined electrical potential via the brush.
As the charger is electrified however, the conductive fibers of the brush do not contact the surface of the photosensitive drum consistently, due to subtle length variations thereof. Further, it is difficult to maintain a regular spacing between the fibers. Thus, electrical potential varies across the surface of the photosensitive drum, and the photosensitive drum's surface is charged unevenly. This uneven charging degrades the quality of the final image.